It has been a point of confusion for some people that want to work on power system, especially those that works on solar and inverter system, some so called Solar Installers have confused their clients and exposed them to unnecessary expenses due to wrong calculation on power. They easily get confused when they want to convert watts to VA.
The simply method to know the power rating of any appliance is by look at the label on the such device or appliance, this will give more details about rating of the appliance.
Almost all electrical devices are rated in power (kW or W), and some will just have the Voltage V, and Current I, with this rating, it’s make it possible to know the wattage P of such appliance by multiply give Volts V and Ampere I
P = V x I
For instance, A 32″ LED TV has ratings as Voltage, 220V and Current, 0.6A
P = 220 x 0.6
P = 132W
Now, let’s try to bring up some definitions like apparent or ideal power, reactive power, actual power and power factor
Apparent Power is simply means the total power in use in a system, it’s Volt Ampere (VA), kilo Volt Ampare (kVA) or Mega Volt Ampere (MVA) as its measuring unit.
Reactive Power, this is simply means the power loss during the conversion from actual to apparent power. It is the power that’s not being used, which is wasted. It’s measuring unit of kVAR
Real or Actual Power, this means as it sounds, it is the actual output power in an electrical device after all the loss that occurs. It’s usually has rated in Watts (W), kilo Watts (kW) or Mega Watts (MVA)
Power Factor is a factor using in measuring of electrical system efficiency. It is use when converting kW to kVA and vice versa. Electrical efficiency has range in between 0 to 1, if the power factor is very near to 1 shows how efficiently is the total output of the electrical system. Mostly 0.8 has been power factor for many inverter systems
Also, there is no need for conversion of kW to kVA in DC circuit and as well as AC circuit that has 100% efficiency, it’s mostly not possible to have it AC circuit
Conversion of kW to kVA; Real power, kW / Power Factor, p.f = Apparent power, kVA
A 32″ LED Television has 132W and a ceilling fan has 65W. Total wattage is (132+65) = 197W
197W/0.8 = 246.25VA
Conversion of kVA to kW; Apparent power, kVA x Power Factor, p.f = Actual power, kW
What is the actual power output of 3.5kVA inverter system.
3500VA x 0.8 = 2800W i.e 2.8kW
The same steps applies in all electrical devices, hence, it’s easier to know what you are powering in the house, except for some appliances that required a starting current or surge which we will discuss in our future post.
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